1. Field of the Invention
The present invention relates to the field of the cooling of a projector, and more particularly to a cooling apparatus of a color wheel for color separation in a single plate type projector and a projection system using the projector. The cooling apparatus comprises an airflow generator, thereby cooling the color wheel and a rod lens of the single plate type projector.
2. Description of the Related Art
A general projector comprises three picture displays. The picture display may be a projective liquid crystal display (LCD), a digital micro-mirror display (DMD), or a reflective liquid crystal display (LCD). Each of light sources including red, green, and blue colors is provided to a corresponding one of three picture displays. Then, the projector combines the colors, thereby displaying a picture. However, a single plate type reflective projector comprises one picture display. The light sources including red, green, and blue colors are provided to the single picture display in a time-sharing mode or in a blocked scroll mode, thereby outputting a synchronized picture signal. That is, the single plate type reflective projector refers to a projector for displaying a color picture using one picture display.
FIG. 1 is a schematic view showing an optical arrangement in a conventional reflective projector.
With reference to FIG. 1, the conventional reflective projector comprises a lamp 100, a color wheel 110, a rod lens 120, a first lens 130, a reflecting mirror 140, a second lens 150, a prism 160 with a panel 161, and a projecting lens 170.
The color wheel 110 serves to separate light generated by the lamp 100 into three colors, i.e., red, green, and blue colors. Herein, the light generated by the lamp 100 is metal halide or xenon.
The color wheel 110 is rotated by a driving gear (not shown). Three filters corresponding to each color such as red, green, and blue are distributed on the color wheel 110 into equal parts.
The rod lens 120 serves to irregularly reflect incident light, thereby mixing the incident light and generating uniform light. The light passing through the rod lens 120 is provided to the panel 161 of the prism 160 via an optical system including the first lens 130, the reflecting mirror 140, and the second lens 150, thereby reflecting a synchronized picture signal and expensively projecting the signal through the projecting lens 170.
In this case, in order to control the shape of focused light, instead of a fly eye lens (FEL), the projector uses the rod lens 120. Therefore, the light generated by the lamp 100 is focused on a plane of incidence of the rod lens 120 having a small area.
FIGS. 2a and 2b show a color wheel of a conventional reflective projector in detail.
With reference to FIGS. 2a and 2b, the light generated by a lamp 210 passes through the color wheel 220. At this time, the color wheel 220 serves to separate the light generated by the lamp 210 into plural colors. The separated light is incident on a plane of incidence of a rod lens 230.
FIG. 2a is a perspective view of the color wheel 220 of the conventional reflective projector, and FIG. 2b is a cross-sectional view of the color wheel 220 of the conventional reflective projector.
As shown in FIG. 2b, the light generated by the lamp 210 passes through the color wheel 220 and is focused on the plane 231 of incidence of the rod lens 230, thereby overheating a plane 221 of the color wheel 220 as well as the plane 231 of incidence of the rod lens 230.
A glass with high refractivity, such as BK-7 which is used as lens material, has a heat resistance, to a maximum temperature of about 400. A color separation filter used in the color wheel is generally made of polymer and has a heat resistance, to a maximum temperature of about 200.
The color wheel 220 is rotated by the driving gear (not shown). The rotation of the color wheel 220 increases the incident area of light. Airflow generated by the rotation of the color wheel 220 provides a cooling effect to the color wheel 220 itself. Therefore, during the operation of the projector, the color wheel 220 can be cooled itself to some degree.
However, during the operation of the projector, a large quantity of the light is always focused on the small area of the rod lens 230, i.e., the plane 231 of incidence. Therefore, although the material of the rod lens 230 has a heat resistance greater than that of the color wheel 220, the rod lens 230 is not high in heat resistance. Particularly, when the plane 231 of incidence of the rod lens 230 is coated, the resistance to thermal degradation of the coating layer cannot be assured.
Recently, a brighter projector has been required more and more. In order to satisfy this recent trend, a high-powered lamp is required. In this case, a color separation system including the color wheel and the rod lens of the single plate type optical system further demands a cooling apparatus for cooling the color wheel and the rod lens.